The term Compact Secondary Substation (CSS) is typically used for trans-former stations in which the power from the main electricity net is transformed from medium voltage, which is in the range 12-24 kV, to low voltage, which is in the range of 100-1000 volts. Typical CSS are produced with a concrete foundation and a concrete or metal housing on top of the foundation. Examples of typical prior art CSS are shown in FIG. 1a and FIG. 1b. Prior art CSS systems are to a certain degree modular in as much as part of the walls of the CSS may be extended by metal profiles to the desired length of a station. When the correct configuration has been achieved, a roof is placed on top of the walls, where the roof is assembled of typically two modules or made in one piece, if the station is of relatively small dimensions.
The modular wall concept implies a certain degree of flexibility, because lengths of CSS can be varied by similar wall sections and adapted to the length of the foundation, which, normally, comes in few certain predetermined model lengths. An assembly, where the length can be freely chosen is not possible, because the roofs are only delivered in certain lengths and because part of the side walls along the foundations does not follow the modular metal profiles with respect to partition.
However, in line with the increasing demands for different types of CSS in different countries, there is an aim for even greater flexibility when it comes to CSS construction.